Windmills may be provided with a windmill pitch driving apparatus that is used as a driving apparatus for controlling the pitch angle of a blade that is rotationally provided on the main shaft portion of the windmill. With recent trends such as increased windmill sizes and increased blade diameters, a situation has arisen where there is a demand for a windmill pitch driving apparatus with high-output specifications having improved output torque. Meanwhile, windmill pitch driving apparatuses are also required to have a smaller configuration because there is only limited space in a windmill for installing the windmill pitch driving apparatuses.
In view of this, an eccentric speed reducer provided with external teeth that rotate eccentrically, as disclosed in PTL 1, is known as an example of a windmill pitch driving apparatus capable of achieving a high speed reduction ratio, which is necessary to improve output torque and reduce size. In the windmill pitch driving apparatus disclosed in PTL 1, an output pinion (530) is attached to an output shaft (374). A plate member is fixed to the end of the output shaft with bolts and regulates pinion movement in the axial direction of the output shaft.